The drop of ruminal pH and heat are common physicochemical stressors challenging ruminal microbiota, nutrient digestion and cattle performance. We characterized the ruminal microbiota and digestive activity in response to different pH (6.0 and 6.6) and temperature (39.5 and 42 °C), as well as established the effective dose of alkaloid supplementation (0, 0.088 and 0.175% of feedstock DM) to modulate ruminal fermentation under these conditions. The acidotic condition decreased microbial diversity and abundances of minor bacterial families whereas most of the highly abundant families like Lactobacillaceae, Prevotellaceae, and Bifidobacteriaceae thrived under the stress. Abundances of all three methanogenic archaea taxa detected increased with heat, as did methane production. However, while Methanomassiliicoccaceae benefited from the low pH, Methanomicrobiaceae diminished and methane production decreased. The low dose of alkaloid addition shifted the fermentation to more propionate and less acetate and the high dose decreased methane and ammonia concentration under the low pH. In conclusion, physicochemical stressors shape the microbial community and function. Mixed alkaloid supplementation facilitates the activity of rumen microbial community under acidotic stress.

瘤胃pH值和热量的下降是挑战瘤胃微生物，营养物质消化和牛性能的常见理化应激源。我们对不同pH（6.0和6.6）和温度（39.5和42°C）的瘤胃微生物群和消化活性进行了表征，并确定了有效剂量的生物碱补充剂（0、0.088和0.175％的原料DM）在这些条件下调节瘤胃发酵。酸中毒状态降低了次要细菌家族的微生物多样性和丰富度，而大多数高度丰富的家族，如乳杆菌科，前荚果科和双歧杆菌科在压力下蓬勃发展。检测到的所有三个产甲烷古细菌类群的丰度随着热量的增加而增加，甲烷的产生也随之增加。但是，尽管甲烷甲烷菌科受益于低pH值，但甲烷微菌科却减少了，甲烷产量降低了。低剂量的生物碱添加使发酵转移到更多的丙酸酯和更少的乙酸盐，而高剂量则降低了低pH下的甲烷和氨气浓度。总之，物理化学应激源决定了微生物群落和功能。混合生物碱补充剂在酸中毒胁迫下促进瘤胃微生物群落的活性。